docs: def merge_code(left_code, right_code):
      """
      { relative_line:
        ((left_abs_line, ((offset, op, args), ...)),
         (right_abs_line, ((offset, op, args), ...))),
        ... }
      """
  
      data = dict()
  
      code_lines = (left_code and left_code.iter_code_by_lines()) or tuple()
      for abs_line, rel_line, dis in code_lines:
          data[rel_line] = [(abs_line, dis), None]
  
      code_lines = (right_code and right_code.iter_code_by_lines()) or tuple()
      for abs_line, rel_line, dis in code_lines:
          found = data.get(rel_line, None)
          if found is None:
              found = [None, (abs_line, dis)]
              data[rel_line] = found
          else:
              found[1] = (abs_line, dis)
  
      return data